Method of recovering separate fiber fractions from corrugated board

ABSTRACT

Method for separating the fiber fraction forming the corrugated medium, having low moisture resistance or high water receptivity, from the fiber fraction forming the linerboard, having high moisture resistance or low water receptivity of corrugated board stock. The stock in a dry state is reduced first to intermediatesized pieces. Subsequently, the pieces are dispersed in water. The temperature of the water, the use of additives, the energy level input and time of dispersion are adjusted to reduce the corrugated medium to small pieces or fibers while retaining the liner board as an essentially intact fraction. The two fractions are then physically separated and recovered.

United States Patent [191 Iannazzi [451 May 20, 1975 [75] Inventor:

[73] Assignee: Arthur D. Little, Inc., Cambridge,

Mass.

22 Filed: July 5,1974

211 App]. No.: 486,073

Related U.S. Application Data [63] Continuation of Ser. No. 291,950, Sept. 25, 1972,

Fred D. Iannazzi, Andover, Mass.

abandoned.

[52] US. Cl 162/4; 162/5 [51] Int. Cl D21c 5/02 [58] Field of Search 162/4, 5, 158, 8; 241/28; 209/3, 4, 9, 133, 268

[56] References Cited UNITED STATES PATENTS 2,641,164 6/1953 Hill et a1. 162/4 2,697,661 12/1954 Hollis 162/4 2,776,209 11/1957 OFlynn et a1. 162/5 2,912,174 11/1959 Bidwell 241/28 X 2,972,171 2/1961 Heritage 241/28 3,301,745 1/1967 Coppick et a1. 241/28 X 3,352,745 1l/1967 Malm 241/28 X 3,499,823 3/1970 Croon et a1 162/158 3,620,909 11/1971 Gleason ..162/4 OTHER PUBLICATIONS Pulp & Paper Manufacture, Vol. 2, Stephenson, McGraw-Hill, Toronto, 1952, pg. 27.

Kinne, M. R., A System for Reclaiming Vinyl Coated Fibers, Tappi, Vol. 39, No. 8, 8-56, pp. 168 A, 169 A.

Primary ExaminerS. Leon Bashore Assistant Examiner-William F. Smith Attorney, Agent, or Firm-Bessie A. Lepper [5 7] ABSTRACT Method for separating the fiber fraction forming the corrugated medium, having low moisture resistance or high water receptivity, from the fiber fraction forming the linerboard, having high moisture resistance or low water receptivity of corrugated board stock. The stock in a dry state is reduced first to intermediate-sized pieces. Subsequently, the pieces are dispersed in water. The temperature of the water, the use of additives, the energy level input and time of dispersion are adjusted to reduce the corrugated medium to small pieces or fibers while retaining the liner board as an essentially intact fraction. The two fractions are then physically separated and recovered.

20 Claims, No Drawings METHOD OF RECOVERING SEPARATE FIBER FRACTIONS FROM CORRUGATED BOARD This is a continuation, of application Ser. No. 291,950, filed Sept. 25, 1972 now abandoned.

This invention relates to a method for separating two type of fibers found in a paper composites and more particularly to separating the semichemical fiber constituent from the kraft fiber constituent in corrugated board in the recycling of corrugated boxes and the like.

In the recovery of secondary fibers from a composite of paper or of a paperboard product such as container board, it is necessary to be able efficiently to separate the constituent fibers to obtain maximum utility of each type of recovered fibers.

Conventional corrugated board comprises two outer layers of liner board made of softwood kraft fibers and an inner layer of corrugated medium formed of hardwood semichemical fibers. The function of the outer layers of linerboard is to provide the packaging material with high resistance to punctures and tears. The linerboard makes up approximately two-thirds of the total weight of the container board and has outstanding high strength characteristics. The principal function of the corrugated medium is to provide impact resistance to the corrugated board, and by comparsion with the linerboard it has poor physical strength characteristics. The semichemical corrugated medium has a low moisture resistance or high water receptivity, while the kraft linerboard has a high moisture resistance or low water receptivity. This marked difference in water receptivity and strength characteristics of the two constituents of corrugated board are used in the separation method of this invention.

In the present known processes for recycling corrugated board, old corrugated boxes and the like (shredded or whole) are thoroughly mixed into water to be dispersed and formed into a plup slurry. Usually, such a slurry contains about 5% by weight of fibrous material and 95% by weight of water. In forming the fiber slurry by this prior art process, the semichemical fibers from the corrugated medium fraction and the kraft fibers from the linerboard fraction become intimately mixed. Since there is no satisfactory Way of separating these two kinds of fibers they must be processed and reused as a fiber mixture. This fiber mixture is cleaned to remove heavy inorganic materials and then treated with a mild cooking action to disperse contaminants such as asphalt, plastics and the like. The resulting fiber mixture can then be formed into either recycled linerboard called jute' liner or recycled corrugated medium called bogus medium" depending upon the process conditions used. In spite of the fact that different process conditions are used, it has been demonstrated that the presence of both types of fibers in the manufacture of either type of product is detrimental to the attainment of the characteristics desired in the products. More specifically, the presence of semichemical fibers in jute linerboard detracts from its physical strength; while the presence of kraft fibers in the bogus medium is detrimental to attaining the desired degree of stiffness.

The difficulties encountered in using such a fiber mixture in producing reconstituted corrugated board have led to a number of different attempts to effect an efficient, enconomic separation of the semichemical fibers from the kraft fibers. For example, in one known experimental process, the pulp slurry containing both kinds of fibers is passed through a centrifugal separator to segregate the long softwood kraft fibers from the short hardwood semichemical fibers. However, it is believed that this process has not been demonstrated to be economically feasible.

It is therefore apparent that there is need for an efficient, economic method for processing corrugated board to be recycled so that a substantial portion of the two types of fiber constituents can be separated and reused to the best advantage.

It is therefore a primary object of this invention to provide a method for separating and recovering the semichemical fibers and the kraft fibers in corrugated board which is being recycled and reconstituted. It is another object to prove a method of the character described which produces two types of recovered fibers which may be used to the best advantage in forming reconstituted corrugated board, the properties of which approximate those of corrugated board made from all virgin fibers. Other objects of the invention will in part be obvious and will in part be apparent hereinafter.

By the method of this invention, the corrugated board stock material (boxes, separators, clippings etc.) are first subjected to a treatment which reduces the material to intermediate-sized pieces, preferably of substantially uniform size. Then the pieces, after being treated with a debonding agent if desired, are introduced into water, which may contain a surfactant, and the resulting dispersion is subjected to mechanical action to achieve differential size reduction. The temperature of the water, the surfactant content and the time of and energy input into the mechanical action are adjusted so as to reduce the corrugated medium constituent to much smaller pieces while retaining substantially all of the linerboard constituent relatively intact in the form of larger pieces. The smaller-sized pieces and fibers of the corrugated medium constituent are then separated from the larger-sized pieces of linerboard constituent such as by conventional screening techniques. Each fraction is then subjected to well-known procedures for disintegration to fiberize the separated fractions. Hand sheets made from fibers from these two fractions show marked differences in physical properties, thus providing evidence that the separation of the semichemical fibers from the kraft fibers is efficient.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others thereof, which will be exemplified in the method hereinafter disclosed, and the scope of the invention will be indicated in the claims.

The corrugated stock which is to be reclaimed and recycled may be such material as old boxes, corrugated scrap, sheets, box dividers and the like. It is preferably first sorted to remove such extraneous material as metal, cloth, dirt and the like. Then the corrugated board is reduced to intermediate-sized pieces, the dimensions on any one side of the pieces ranging from about one to six inches giving the pieces two surfaces ranging in area from about 1 to 36 square inches. It is preferable that substantially all of these pieces for any one batch or run be of substantially uniform size, e.g., about 1 X l, 1 X 6, 2 X 2, 2 X 6, etc. It will, of course, be appreciated that these sizes are only exemplary and very approximate. Uniformity of dimensions is preferable to ensure that substantially all of the intermediatesized pieces receive essentially the same treatment over a given period of time during the differential size reduction step. Thus, for example, if these intermediate-sized pieces were made up of a mixture of pieces which where l X 1 inch, 3 X 3 inches and 6 X 6 inches it becomes readily apparent that it would require different lengths of time for water to penetrate into the central portions of the corrugated mediums of these three differently sized pieces. Since the time over which mechanical working is performed is one important parameter in the differential size reduction step, it is apparent that it is preferable not to introduce an additional factor of wide size range of the intermediate-sized pieces into the determination of the various operating parameters of this step.

During the step of reducing the corrugated board stock to intermediate-sized pieces it may be desirable to add a small amount of a chemical debonding agent to the stock to reduce the possibility of undesirable fiber damage. Such a debonding agent is exemplified by water or a dilute water solution of urea, of ethylene carbonate, of a mixture of urea and ethylene carbonate or of a surfactant. The amount of such a chemical bonding agent solution should not exceed about percent by weight of the corrugated stock.

The step of reducing the corrugated board stock to the intermediate-sized pieces may be performed in one of several commercially available types of equipment. For example, a suitable size reduction mill such as a hammermill or a rotary cutter may be used. The latter is preferable since it produces pieces of corrugated board which have edges that are clean cut and uncompacted. Such edges permit the water, in which the pieces are dispersed, readily to penetrate into and through the corrugated medium to free it for reduction into small pieces.

After the corrugated board stock has been reduced to the intermediate-sized pieces, the pieces are subjected to a differential size reduction step in which the semichemical corrugated medium constituent is materially reduced in size while the kraft linerboard constituent is retained in substantially its intermediate-sized condition. This differential size reduction step is carried out by dispersing the intermediate-sized pieces in water which may contain a surfactant. The amount of corrugated board stock dispersed in water may range from about /2 to 10 percent by weight of water used. If a surfactant is used it may be an anionic, cationic or nonionic material, and it may range in amount between about 0.1 to about 0.3 percent based on the weight of the water. The water into which the intermediate-sized pieces are introduced for dispersing may range in temperature from ambient temperature up to about 160F.

Once the pieces of corrugated board stock are introduced into the water for dispersion they are subjected to what may be termed low-energy mechanical action, the purpose of which is to separate the corrugated medium from the linerboard and to disperse the more water-receptive corrugated medium constituent into individual fibers or into small pieces, e.g., up to about A to inch in size while the more water-resistant (less water-receptive linerboard constituent remains essential intact in the size of the original intermediate-sized feed stock or is reduced to pieces considerably larger than inch.

If the differential size reduction step is carried out as a batch operation, exemplary types of suitable equipment include, but are not limited to, a pulper, a propeller-type mixer operating between about 20 and rpm, and a ball mill with glass balls ranging in size from about A to /8 inch in diameter. If this step is carried out as a continuous operation, exemplary types of suitable equipment include, but are not limited to, a pipeline type mixer wherein residence time is controlled by controlling the back-pressure and a continuous ball mill.

It is necessary to control the operational parameters in combination to obtain the dispersion of the corrugated medium semichemical fibers while minimizing the dispersion of the kraft fibers of the linerboard. It is desired that if good differentiation of properties is to be maintained in the finally separed constituents that not more than about 20 percent of the kraft fibers originating from the liner board constituent be dispersed. It is, however, preferable that this fraction of dispersed kraft fibers be kept at 10 to 15 percent or below. Ideally, of course, it would be most preferable if none of the kraft fibers were dispersed, but this is difficult to attain.

The operational parameters which must be adjusted to attain the desired dispersion as described are water temperature, surfactant content, the time period over which the mechanical action is applied and the level of energy input into the applied mechanical action. These parameters in combination must be adjusted to obtain the desired degree of dispersion. Some examples may be cited for guidance but not for placing limitations on any one parameter. lf ambient temperature water is used containing a low concentration of surfactant and a low-level of energy input is employed, then the dispersing time may be several minutes, e.g., two to six minutes. If, on the other hand, the water is at an elevated temperature, the surfactant is present at a relatively high concentration and the energy level input is greater, then the time required to achieve the desired degree of differential size reduction may be reduced to a minute or even less. Therefore, knowing the results (type of dispersion) required, the range of surfactant concentration, and the upper limit on dispersion water temperature, it is well within the skill of the art to determine residence time in any suitable equipment for any desired intermediate-sized pieces of corrugated stock being processed.

After the attainment of the desired differential size reduction, the resulting slurry, containing as one fraction the small pieces or fibers of corrugated medium semichemical fibers and as the other fraction the intermediate-sized pieces of liner-board, is subjected to a separation step whereby the two fractions are separated. This may be accomplished by use of a wellknown continuously moving inclined screen or a rotary screen apparatus wherein the small pieces or fibers of the corrugated medium along with a small amount of the linerboard pass through the screen for collection and the larger-sized pieces of the linerboard are retained on the screen for separate collection. Alternatively, a vibrating screen apparatus may be used. It is also possible to employ apparatus based upon a flotation technique in which the larger pieces float to the surface of a flotation cell where they are skimmed off and thereby separated from the fraction of small pieces and fibers which sink to the bottom. During this separation step it may be preferable or necessary to dilute the slurry to a consistency best suited for the particular type of separation apparatus used. Typically, consistencies of from about 0.1 to 5 percent will be satisfactory.

The choice of an optimal consistency is within the skill of the art.

Once the two types of fibers have been separated they are handled in a conventional manner to be reprocessed into corrugated medium and linerboard. Alternatively, the recovered fiber fractions can be used for the manufacture of other types of paper or paperboard materials. For example, since the linerboard is formed of high quality fibers, this frraction formed primarily of softwood kraft fibers may be bleached and used in high-value paper products.

The method of this invention may be described in further detail with reference to the following example which is meant to be illustrative and not limiting.

The stock used was obtained from old container board (corrugated board). After a preliminary cleaning, the container board was cut up into intermediatesized pieces which were generally uniform in size averaging out about one by one inch in dimension. In forming the intermediate-sized pieces a paper cutter was used. No debonding agent was added during this step. The intermediate-sized pieces were then added to water at room temperature (about 64F) which did not contain any surfactant. The amount of corrugated stock was 2 percent by weight of water used. This material was processed in a laboratory stirrer operating at 60 rpm for 5 minutes. The resulting slurry was diluted to a consistency of about [2 percent and the fiber fractions were separated by passing the slurry through a screen, the openings in which were /2 X /.2 inch. Each fiber fraction was then formed into a papermaking furnish following TAPPI Standard Method No. 410 for dispersing fibers for forming hand sheets. Hand sheets were then formed from the two furnishes on a Noble- Wood apparatus. The sheets were conditioned overnight at 50 percent relative humidity and subjected to standard test procedures to obtain the results tabulated in Table l. For comparison, a hand sheet was also formed of a combination of semichemical and kraft fibers obtained from a sample of the corrugated stock. The procedures for dispersing the fibers and forming the hand sheet were the same method as described.

Table 1 tion shall be interpreted as illustrative and not in a limiting sense. 1 claim:

1. A method for separating the semichemical fiber fraction forming the corrugated medium from the kraft fiber fraction forming the linerboard in corrugated board, comprising the steps of a. reducing corrugated board stock to intermediatesized pieces no larger than about six inches in any one dimension;

b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein; subjecting said corrugated stock in water to differential size reduction by mechanical action, the temperature of said water and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pieces no larger than about three-eights inch in any one dimension while retaining substantially all of the kraft linerboard fraction in the form of larger or intermediate-sized pieces; and separating said fibers and small pieces of said semichemical corrugated medium fraction from said kraft linerboard fraction.

2. A method in accordance with claim 1 including the step of adding a debonding agent to said corrugated board stock prior to said reducing step (a) thereby to minimize fiber breaking.

3. A method in accordance with claim 1 including the step of adding a surfactant to said water prior to step (b), the concentration of said surfactant being up to about 0.3 percent by weight of said water.

4. A method in accordance with claim 1 wherein said corrugated board stock is reduced in size to form said intermeidate-sized pieces with dimensions ranging between about 1 and 6 inches.

5. A method in accordance with claim 1 wherein the amount of said corrugated board stock added to said water ranges between about 1 and 10 percent by weight of said water.

Physical Strength Characterists of Fibers Reclaimed from Corrugated Board Total Wt. Mullen of Fraction Weight Free- Tensile Tear Fraction (psi) (gm) (gm)* ness* lbs./l in. (gm) Composite 16.0 41.1 2.68 570 8.2 83 Linerboard 18.2 69.0 2.65 610 11.2 116.6 Corrugated 8.25 31.5 2.64 650 6.6 32

medium 64 square inches Canadian Standard Frccncss The physical data of Table 1 clearly show that the two fiber fractions possess markedly different strength properties, particularly tensile and tear strengths. These differences are evidence that the two types of fibers semichemical from the corrugated medium and kraft from the linerboard were effectively separated by the method of this invention.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description are efficiently attained and, since certain changes may be made in carrying out the above method without departing from the scope of the invention, it is intended that all matter contained in the above descrip- 6. A method in accordance with claim 1 wherein the temperature of said water used to form said dispersion ranges between ambient temperature and about F.

7. A method in accordance with claim 1 wherein said mechanical action is carried out over a period of time ranging from a few seconds to several minutes.

9. A method for separating the semichemical fiber fraction forming the corrugated medium from the kraft fiber fraction forming the linerboard in corrugated board, comprising the steps of a. reducing corrugated board stock to intermediatesized pieces having dimensions ranging between about 1 and 6 inches;

b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein, said water containing up to about 0.3 percent by weight of a surfactant and being at a temperature between ambient temperature and 160F, the amount of said corrugated board stock added to said water ranging between about 1 and 10 percent by weight of said water;

0. subjecting said corrugated stock in water to differential size reduction by mechanical action, the temperature of said water, the amount of said surfactant, the dimensions of said corrugated stock pieces, and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pices, no greater than about /8 inch in size while retaining substantially all of the kraft linerboard fraction in the form of larger or intermediate-sized pieces; and separating said fibers and small pieces of said semichemical corrugated medium fraction from said kraft linerboard fraction. V

10. A method in accordance with claim 9 including the step of adding a debonding agent to said corrugated board stock prior to said reducing step (a) thereby to minimize fiber breaking.

11. A method in accordance with claim 9 wherein said mechanical action is carried out over a period of time ranging from a few seconds to several minutes.

12. A method for separating the semichemical fiber fraction forming the corrugated medium from the kraft fiber fraction forming the linerboard in corrugated board for recycling into paper products, comprising the steps of a. reducing corrugated board stock to intermediatesized pieces no larger than about six inches in any one dimension;

b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein;

c. subjecting said corrugated stock in water to different size reduction by mechanical action, the temperature of said water and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pieces no larger than about three-eights inch in any one dimension while retaining substantially all of the kraft linerboard fraction in the form of larger or intermediate sized pieces;

. separating said fibers and small pieces of said semichemical corrugated medium fraction from said kraft linerboard fraction; and

e. separately dispersing said semichemical corrugated medium and said kraft linerboard fractions in water to form separate papermaking furnishes.

13. A method in accordance with claim 12 including the step of adding a debonding agent to said corrugated board stock prior to said reducing step (a) thereby to minimize fiber breaking.

14. A method in accordance with claim 12 including the step of adding a surfactant to said water prior to step (b), the concentration of said surfactant being up to about 0.3 percent by weight of said water.

15. A method in accordance with claim 12 wherein said corrugated board stock is reduced in size to form said intermediate-sized pieces with dimensions ranging between about 1 and 6 inches.

16. A method in accordance with claim 12 wherein the amount of said corrugated board stock added to said water ranges between about 1 and 10 percent by weight of said water.

17. A method in accordance with claim 12 wherein the temperature of said water used to form said dispersion ranges between ambient temperature and about 160F.

18. A method in accordance with claim 12 including the further step of forming from said papermaking furnishes reconstituted papers suitable for corrugated medium and for linerboard in the manufacture of corrugated board.

19. A method for separating the fiber fraction forming the corrugated medium, having low moisture resistance or high water receptivity, from the fiber fraction forming the liner-board, having high moisture resistance, or low water receptivity, in corrugated board, comprising the steps of a. reducing corrugated board stock to intermediate sized pieces no larger than about six inches in any one dimension;

b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein;

0. subjecting said corrugated stock in water to differential size reduction by mechanical action, the temperature of said water and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pieces no larger than about three-eights inch in any one dimension while retaining substantially all of the linerboard fraction in the form of larger or intermediate-sized pieces; and

d. separating said fibers and small pieces of said corrugated medium fraction from said linerboard fraction.

20. A method for separating the fiber fraction forming the corrugated medium, having low moisture resistance or high water receptivity, from the fiber fraction forming the linerboard, having high moisture resistance or low water receptivity, in corrugated board for recycling into paper products, comprising the steps of a. reducing corrugated board stock to intermediatesized pieces no larger than about six inches in any one dimension; b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein; c. subjecting said corrugated stock in water to differential size reduction by mechanical action, the temperature of said water and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pieces no larger than about three-eighths inch in any one dimension while retaining substantially all of the linerboard e. separately dispersing said corrugated medium and said linerboard fractions in water to form separate papermaking furnishes. 

1. A method for separating the semichemical fiber fraction forming the corrugated medium from the kraft fiber fraction forming the linerboard in corrugated board, comprising the steps of a. reducing corrugated board stock to intermediate-sized pieces no larger than about six inches in any one dimension; b. introduCing said intermediate-sized pieces of corrugated stock into water for dispersion therein; c. subjecting said corrugated stock in water to differential size reduction by mechanical action, the temperature of said water and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pieces no larger than about three-eights inch in any one dimension while retaining substantially all of the kraft linerboard fraction in the form of larger or intermediate-sized pieces; and d. separating said fibers and small pieces of said semichemical corrugated medium fraction from said kraft linerboard fraction.
 2. A method in accordance with claim 1 including the step of adding a debonding agent to said corrugated board stock prior to said reducing step (a) thereby to minimize fiber breaking.
 3. A method in accordance with claim 1 including the step of adding a surfactant to said water prior to step (b), the concentration of said surfactant being up to about 0.3 percent by weight of said water.
 4. A method in accordance with claim 1 wherein said corrugated board stock is reduced in size to form said intermeidate-sized pieces with dimensions ranging between about 1 and 6 inches.
 5. A method in accordance with claim 1 wherein the amount of said corrugated board stock added to said water ranges between about 1 and 10 percent by weight of said water.
 6. A method in accordance with claim 1 wherein the temperature of said water used to form said dispersion ranges between ambient temperature and about 160*F.
 7. A method in accordance with claim 1 wherein said mechanical action is carried out over a period of time ranging from a few seconds to several minutes.
 8. A method in accordance with claim 1 wherein said separating comprises collecting said kraft linerboard fraction on a screen sized to permit said corrugated medium fraction to pass therethrough.
 9. A method for separating the semichemical fiber fraction forming the corrugated medium from the kraft fiber fraction forming the linerboard in corrugated board, comprising the steps of a. reducing corrugated board stock to intermediate-sized pieces having dimensions ranging between about 1 and 6 inches; b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein, said water containing up to about 0.3 percent by weight of a surfactant and being at a temperature between ambient temperature and 160*F, the amount of said corrugated board stock added to said water ranging between about 1 and 10 percent by weight of said water; c. subjecting said corrugated stock in water to differential size reduction by mechanical action, the temperature of said water, the amount of said surfactant, the dimensions of said corrugated stock pieces, and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pices, no greater than about 3/8 inch in size while retaining substantially all of the kraft linerboard fraction in the form of larger or intermediate-sized pieces; and d. separating said fibers and small pieces of said semichemical corrugated medium fraction from said kraft linerboard fraction.
 10. A method in accordance with claim 9 including the step of adding a debonding agent to said corrugated board stock prior to said reducing step (a) thereby to minimize fiber breaking.
 11. A method in accordance with claim 9 wherein said mechanical action is carried out over a period of time ranging from a few seconds to several minutes.
 12. A method for separating the semichemical fiber fraction forming the corrugated medium from the kraft fiber fraction forming the linerboard in corrugated bOard for recycling into paper products, comprising the steps of a. reducing corrugated board stock to intermediate-sized pieces no larger than about six inches in any one dimension; b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein; c. subjecting said corrugated stock in water to different size reduction by mechanical action, the temperature of said water and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pieces no larger than about three-eights inch in any one dimension while retaining substantially all of the kraft linerboard fraction in the form of larger or intermediate sized pieces; d. separating said fibers and small pieces of said semichemical corrugated medium fraction from said kraft linerboard fraction; and e. separately dispersing said semichemical corrugated medium and said kraft linerboard fractions in water to form separate papermaking furnishes.
 13. A method in accordance with claim 12 including the step of adding a debonding agent to said corrugated board stock prior to said reducing step (a) thereby to minimize fiber breaking.
 14. A method in accordance with claim 12 including the step of adding a surfactant to said water prior to step (b), the concentration of said surfactant being up to about 0.3 percent by weight of said water.
 15. A method in accordance with claim 12 wherein said corrugated board stock is reduced in size to form said intermediate-sized pieces with dimensions ranging between about 1 and 6 inches.
 16. A method in accordance with claim 12 wherein the amount of said corrugated board stock added to said water ranges between about 1 and 10 percent by weight of said water.
 17. A method in accordance with claim 12 wherein the temperature of said water used to form said dispersion ranges between ambient temperature and about 160*F.
 18. A method in accordance with claim 12 including the further step of forming from said papermaking furnishes reconstituted papers suitable for corrugated medium and for linerboard in the manufacture of corrugated board.
 19. A METHOD FOR SEPARATING THE FIBER FRACTION FORMING THE CORRUGATED MEDIUM, HAVING LOW MOISTURE RESISTANCE OR HIGH WATER RECEPTIVITY, FROM THE FIBER FRACTION FORMING THE LINERBOARD, HAVING HIGH MOISTURE RESISTANCE, OR LOW WATER RECEPTIVITY, IN CORRUGATED BOARD, COMPRISING THE STEPS OF A. REDUCING CORRUGATED BOARD STOCK TO INTERMEDIATE PIECES NO LARGER THAN ABOUT SIX INCHES IN ANY ONE DIMENSION; B. INTRODUCING SAIDINTERMEDIATE-SIZE PIECES OF CORRUGATED STOCK INTO WATER FOR DISPERSION THEREIN; C. SUBJECTING SAID CORRUGATED STOCK IN WATER TO DIFFERENTIAL SIZE REDUCTION BY MECHANICAL ACTION, THE TEMPERATURE OF SAID WATER AND THE LENGTH OF TIME AND ENERGY LEVEL INPUT OF SAID MECHANICAL ACTION BEING ADJUSTED TO SEPARATE SAID CORRUGATED MEDIUM FRACTION TO FIBEERS OR SMALL PIECES NO LARGER THAN ABOUT THREE-EIGHTS INCH IN ANY ONE DIMENSION WHILE RETAINING SUBSTANTIALLY ALL OF THELINERBOARD FRACTION IN THE FORM OF LARGER OR INTERMEDIATE-SIZE PIECES; AND D. SEPARATINNG SAID FIBERS AND SMALL PIECES OF SAID CORRUGATED MEDIUM FRACTION FROM SAID LINERBOARD FRACTION.
 20. A method for separating the fiber fraction forming the corrugated medium, having low moisture resistance or high water receptivity, from the fiber fraction forming the linerboard, having high moisture resistance or low water receptivity, in corrugated board for recycling into paper products, comprising the steps of a. reducing corrugated board stock to intermediate-sized pieces no larger than about six inches in any one dimension; b. introducing said intermediate-sized pieces of corrugated stock into water for dispersion therein; c. subjecting said corrugated stock in water to differential size reduction by mechanical action, the temperature of said water and the length of time and energy level input of said mechanical action being adjusted to separate said corrugated medium from said linerboard and to reduce said corrugated medium fraction to fibers or small pieces no larger than about three-eighths inch in any one dimension while retaining substantially all of the linerboard fraction in the form of larger or intermediate sized pieces; d. separating said fibers and small pieces of said corrugated medium fraction from said linerboard fraction; and e. separately dispersing said corrugated medium and said linerboard fractions in water to form separate papermaking furnishes. 